Kristen Vieira-Lomasney & Nathalie Wong
The Coral Reef
  • What is a coral reef?
  • The importance of the coral reef
  • Food Web
  • Threats
  • Conservation
  • Photo Gallery
  • Bibliography

Threats

20% of the world's coral reefs have been destroyed and show no prospects of recovery...
How are coral reefs endangered? Coral reefs are being destroyed because of human activities, such as pollution and fishing, but also because of natural events, or circumstances, like weather and tidal immersions.

Natural effects

  • Storms
Coral reefs can be damaged by natural events such as hurricanes, cyclones and tsunamis. Wave activity resulting from these storms can beak apart corals. Because storms are a natural part of coral reef ecosystems, coral species should be adapted to this type of disturbance and be able to recover following storms. However, human alteration to the environment has made recovery difficult.
  • Natural temperature changes
Coral reefs require particular environmental conditions for growth and temperatures from 20 to 28 degrees Celsius are optimal for growth. Increasing temperature too much can cause coral polyps to expel the zooxanthellae and lead to coral bleaching. For example, the El Nino Southern Oscillation of 1997-1998 caused severe coral bleaching in the Indo-Pacific with 70-80% of shallow water corals killed in some regions. 
  • Coral disease
 Scientists have identified about 30 diseases of corals. Coral disease can be cause by bacteria, fungi, algae and worms. In the Caribbean reefs, 80% of coral has been lost to disease in the last 20 years. Thre frequency of coral disease has increased significantly over the last 10 years, causing widespread moratlity among reef-building corals, due  to mainly anthropogenic pollutants.
  • Tidal immersions
Long periods of exceptionally low tides leave shallow water coral heads exposed. Corals exposed during daylight hours are subjected to the most ultraviolet radiation, which can overheat and dry out the coral's tissues. Corals may become so physiologically stressed that they begin to expel their symbiotic zooxanthellae, which leads to bleaching and even death. 
Picture
Coral reef exposed and outside of water because of tidal immersion
  • Predation
Corals are vulnerable to predation. Fish, marine worms, barnacles, crabs, snails and sea stars all prey on the soft inner tissues of coral polyps. In extreme cases, entire reefs can be devastated by this kind of predation. 

Though these are natural threats to coral reefs, they have ALL been made infinitely worse by human activity (normally coral reefs would be better adapted to environmental threats)

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Cradle to Myriads of Species Millennia to Create 
Moments to Destroy 
-Jim Morris 

Anthropogenic effects

  • Climate change
Global warming, a reality today in which temperatures, as well as levels of atmospheric CO₂, are rising drastically, brought on by human activity is having devastating effects on coral reefs.  
First of all, corals cannot survive if the water temperature is too high.
Secondly, warming seas and ocean acidification (see next point) are affecting reefs by causing mass coral bleaching events and slowing the growth of coral skeletons.
Thirdly, the warming seas, ocean acidification and mass coral bleaching brought on by climate change is  making infectious disease outbreaks more likely to become more frequent in the, now fragile, coral reef ecosystem. 
Picture
Coral that, due to stress, has become bleached and a coral with black band disease
  • Ocean Acidification
Since the beginning of the Industrial revolution, the release of carbon dioxide from human activities (burning of fossil fuels) has resulted in atmospheric CO₂ concentrations that have increased from 280 to 385 ppm. The ocean absorbs about one third of the additional CO₂generated every year by human activities, which lowers the ocean's pH and increases the ocean's acidity. This acidification of the ocean appears to be dissolving the skeletons of corals. Thus, corals may form weaker skeletons, making them more susceptible to damage from storms, waves, etc. 
  • Sedimentation
Construction (both along coasts and inland), mining, logging and farming along coastal rivers can all lead to erosion. As a result, particles end up in the ocean and cover coral reefs. This smothers coral and deprives it of the sunlight it needs to survive. Additionally,  the destruction of mangrove forests and sea grasses, which normally filter out large amounts of sediment, by humans is exacerbating this problem. 
  • Destructive fishing practices
Many current fishing practices are destructive and unsustainable. These practices include: cyanide fishing, blast fishing, bottom trawling, muro-ami and overfishing. 
Cyanide fishing: Fishermen dive down to the reef and squirt cyanide in coral crevices and on the fast-moving fish, to stun the fish, making them easy to catch. The cyanide poisons and kills most fish, including coral polyps, symbiotic algae and other small organisms necessary for healthy reefs. In addition, the fishermen rip apart the coral reefs with crowbars in order to catch the fish that have taken refuge in the reefs. 
Blast fishing: Fishermen use underwater explosions to damage the swim bladders of fish so that they float to the surface where they are easily captured. The blast of the explosions destroys coral and flattens the reef structure. 
Bottom trawling: Fishermen drag a fishing net along the sea bottom. Reefs in the net's path get mowed down; Long, wide patches of rubble and sand are all that is left in their wake. Also, fishing nets left as debris can be problematic in areas of wave disturbance; In shallow water, live corals become entangled int hese nets and are torn away from their bases and these nets can strange thousands of fish, sea turtles and marine animals. 
Muro-ami: This style of fishing involves scaring the fish into a net by pounding on the coral reef with sticks or other heavy objects that severely damage the coral reef.
Overfishing: Often, too many fish are taken from one coral reef to sustain a population in that area. In 1950, no fisheries were reported as being over exploited  whereas by 1996, 35% of fisheries were reporting over-exploitation and an additional 25% were reported as being near over-exploited. Over-fishing can reduce genetic variation in a population, making it harder for species to adapt to environmental change and  mate. In addition, over-fishing can alter trophic interactions and cause unexpected indirect effects on the environment (see "Indirect ecological effects")
  • Indirect ecological effects
Species can affect other species directly by eating them or serving as food. But, they can affect each other indirectly as well. For example, removing a predator might harm the competitor of a prey species because fewer predators results in a larger population size of its prey which can in turn decrease the population size of its competitor; In short, the removal of even one species (by overfishing for example), can imbalance the entire food web, creating chain reactions and affecting many different species as well. 
One important problem human activity (overfishing) has caused is the decrease in the herbivorous fish populations. Because there are less herbivorous fish to eat the plants (notably the algae), there is more algae. The algae grows much more quickly than the coral. And so, this excess of fast-growing algae will result in the coral being almost suffocated by the algal growth and the sunlight being unable to penetrate the algae and reach the coral. 
  • Water pollution
Reefs are harmed when human, animal and fertilizer is dumped into the ocean, or when a river system carries these pollutants to reef waters. Oil, gas and pesticide contamination poison coral and marine life. Chemical pollution can also be extremely harmful to coral reefs if they occur during coral spawning because the oil can kill eggs and sperm.  Pollutants, like sewage and agricultural run-off, increase the level of nitrogen around coral reefs, causing an overgrowth of algae which smothers reefs by cutting off sunlight that polyps need to survive. Turtles and other sea animals often mistake plastic bags for jellyfish and eat them. The plastic blocks their digestive tract, causing them to starve to death. Discarded fish nets snag on coral and destroy coral, as well as strangle thousands of fish. Bacteria added by sewage pollution cause increased incidences of coral diseases. The negative effects of water pollution surely do not end there.  
  • Coastal development
Coastal populations have risen which has led to a multitude of problems for coral reefs. Developers have constructed piers and strutcures directly on top of coral reefs, destroying them and endangered the plethora of species that live in them. The coastal development greatly heightened pollution in the reef waters as well. 
  • Coral mining
Live coral is removed from reefs for use as bricks, road-fill or cement for new buildings. Corals are also sold as souvenirs to tourists and to exporters.
  • Careless tourism
Tourist resorts empty their sewage directly into the water surrounding coral reefs which contributes greatly to coral reef degradation. Careless boating, diving, snorkeling, collecting coral and dropping anchors on reefs happens all over the world and contributes greatly to destroying coral reefs as well.

Coral reefs may recover from periodic traumas caused by weather or other natural occurrences. If, however, corals are subjected to numerous and sustained stresses including those imposed by people, the strain may be too much for them to endure, and               the coral reefs will perish.

The above video depicts the startling reality of what is to come to our coral reefs in the very near future. This video depicts life in the year 2065; life without one, single coral reef left on the face of the earth as a result of our terrible greed (human activity). However, we, in the year 2013, are at the turning point of this disaster; We can opt to save our coral reefs. (see Conservation page)

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